During the three years of requested support I propose to: 1. Obtain crystals of troponin or of its calcium binding component (TN-C) suitable for crystallographic study. 2. Obtain crystals of tubulin. 3. Complete the atomic resolution crystal structure determination of either troponin or tubulin, whichever proves more tractable. 4. Pursue the theoretical implications of my model which states that many calcium control proteins contain "EF hands" homologous to those of parvalbumin, TN-C and myosin light chains. 5. Complete the crystal structure determination of the fragment of parvalbumin residues 76 through 108. This is a single "EF hand". 6. Attempt to crystallize other calcium proteins, e.g. S-100, L-1 and L-2 from nervous tissue, which might contain "EF hands".